Explosive composition containing inorganic nitrate salt of particular size distribution



United States Patent EXPLOSIVE COMPOSITION CONTAINING INOR- GANIC NITRATE SALT 0F PARTICULAR SIZE DISTRIBUTION William Don McFerrin, State St., Suite 410, Reno, Nev. 89501 No Drawing. Filed Aug. 22, 1966, Ser. No. 573,806

. 10 Claims. (Cl. 14939) ABSTRACT OF THE DISCLOSURE An explosive composition wherein a desired explosive equivalent relative to blasting gelatine (having a 100% relative weight strength) is effected by using a direct one to one percentage ratio of ammonium nitrate having a critical grain size distribution; wherein the explosion characteristics can be modified by the appropriate substitution of inexpensive ingredients; and wherein the specific gravity of the explosive composition can be altered by the use of preselected indensifying agents to permit of marine and wet bore hole usages.

The invention relates to explosives of the free flowing variety such as are used, for example, in mining, quarrying and highway and bridge construction.

The prior art, as well as the market place, are replete with explosive compositions which perform in a moderately satisfactory fashion. In the main, however, the products heretofore available have failed to provide a family or group of explosives which are not only readily and inexpensively produced but which are at the same time capable of formula modification to provide the desired explosive characteristics for the many and varied situations encountered in the field.

It is therefore an object of the invention to provide an explosive composition and method of producing the same which affords the advantages set forth above and which in all cases provides a cap sensitive explosive capable of detonation by a standard Number 6 cap, and which, therefore, does not require a booster.

It is another object of the invention to provide an explosive in which the desired strength can readily be achieved by varying the percentage of one of the ingredients in a direct, one to one ratio to the explosive equivalent.

It is a further object of the invention to provide an explosive in which inexpensive substitute ingredients can be used to adapt the composition to the varied situations encountered in field operations.

It is still a further object of the invenion to provide an explosive which can be submerged, as for use in wet bore holes and for marine usage.

It is yet a further object of the invention to provide an explosive which can be inexpensively produced owing to the use of commercially available ingredients, yet which affords a high degree of reproduceability with respect to such characteristics as velocity, brisance and gas volume.

It is another object of the invention to provide a generally improved explosive composition.

Other objects, together with the foregoing, appear in the following description of various explosive mixtures and their process of manufacture.

The explosive composition of the invention is of the free 3,378,417 Patented Apr. 16, 1968 flowing, alkali nitrate category and, more particularly, utilizes ammonium nitrate as the predominant ingredient.

As is well known in the explosive art, the strength of an explosive refers to the amount of energy developed upon detonation, as measured, for example, by the Du Pont Ballistic Mortar.

For convenience, the term relative weight strength," or explosive equivalent, is also used herein. Blasting gelatine is defined as having a 100% relative weight strength, and the ratio thereto of the ballistic mortar deflection of a given explosive of the same weight is termed the relative weight strength, or explosive equivalent, of the given explosive.

In other words, a given explosive that deflects the mortar to 90% of the deflection provided by the same weight of blastin gelatine, is said to have a 90% equivalent strength; and, in like fashion, a deflection of 40% of the total deflection afforded by the same weight of blasting gelatine is defined as a 40% explosive equivalent, or as having a 40% relative weight strength.

It is highly desirable to be able to produce, on demand, an explosive affording a desired explosive equivalent as ordered by an expert in the field to meet the Widely varying field conditions of rock sizes and kinds and of various intermixtures of rocks and earth.

I have discovered that by using a predetermined particle size distribution of ammonium nitrate, any desired explosive equivalent, or strength, can be achieved by using a percentage of the prescribed size ammonium nitrate (as a percent of the total composition by weight) numerically equal to the desired explosive equivalent.

In other words, by having 90% of the total composition consist of ammonium nitrate of the prescribed grain size, the composition will have a 90% explosive equivalent, or strength; similarly, using ammonium nitrate results in an explosive having 70% strength, etc.

The foregoing relationship holds true from approximately on the upper end, down to approximately 40% on the lower end.

The prescribed grain size of ammonium nitrate is as follows: in terms of Tyler Sieve measurements, 78% of the ammonium nitrate grains must pass through a 150 mesh screen, and the balance, or 22%, must pass a 100 mesh but are retained by a 150 mesh screen.

The ammonium nitrate granules can be either of random configuration or of spherical configuration.

The random, or irregular, configuration results from subjecting conventional ammonium nitrate prills, or pellets, to a comminution operation, such as in a swinging hammer mill, followed by the step of screening to achieve the prescribed 78% minus 150 mesh and the 22% minus 100 plus 150 mesh distribution.

The spherical configuration granules, on the other hand, are produced by the commercially known process of dissolving ammonium nitrate to form a supersaturated solution, followed by blowing the solution through atomizing nozzles into a drying atmosphere, the resultant product having or even more of the granules in a substantially spherical form. Here again, screening is subsequently effected to give the prescribed 78% minus 150, 22% minus plus size distribution.

Use of the spherical grains affords certain advantages, such as superior loading density resulting from the better nesting effect of the spheres, and the attendant more intimate contact with other particles of ammonium nitrate and with the other ingredients in the total composition.

As previously mentioned, the practical upper limit of explosive equivalent, or strength, of the composition of the present invention is 90%. For an explosive composition having this 90% strength, the following ingredients can be used, in the Weight percentages shown, as a percent of the weight of the total composition:

Example 1 Percent Ammonium nitrate 90 Aluminum powder Dinitrotoluene 4 Granulated cork 1 In Example 1, as Well as in all subsequent examples, the ammonium nitrate is of the previously described particle size distribution.

The aluminum powder, in all cases, is preferably of the kind commercially available, an example being the aluminum powder sold under the trademark Reynolds 400. In these commercial grades, the average aluminum particle size is approximately 23.8 microns, and some of the particles exceed 30 microns in size. For convenience, the aluminum powder will sometimes be referred to as the metal activator, or metal sensitizer, ingredient. Although finely comminuted particles of other metals, such as zinc or magnesium, can be used, aluminum is the preferred metal for the activator or sensitizer ingredient. A range of 5% to 8% metal activator is utilized, it having been i found that especially for some lower strength compositions an amount in excess of 6% is preferable.

The dinitrotoluene can be generally characterized as a nitrobody modifying agent, and, while other such agents can be used dinitrotoluene is an entirely satisfactory representative of the category.

The granulated cork provides the ingredient known generally in the art as the combustible carbonaceous ingredient. Preferably, the cork ingredient consists entirely of commercially available baked and regranulated cork material having a grain size capable of passing a 50 mesh screen.

Another very satisfactory carbonaceous ingredient is commercialy available industrial wood meal, 61% being minus 150 mesh and 39% being plus 150, Tyler Sieve size.

in the event that a 75% explosive equivalent composition is desired, for example, then, as previously described, 75% by weight of the total composition will consist of ammonium nitrate of the prescribed grain size distribution. To this 75% ammonium nitrate is added approximately 6% of metal activator, or metal sensitizer, such as aluminum powder; approximately 4% of nitro-body modifying agent, such as dinitrotoluene (DNT); and approximately 1% of combustible carbonaceous material, such as cork or wood meal.

The foregoing ingredients total 86% leaving a balance of 14%.

One of the major contributions of the present invention is the discovery that by using certain other materials for this balance, various beneficial and unexpected results are provided.

The materials so utilized are conveniently termed substitute materials, or substitute ingredients, in the sense that they are substituted for at least .a portion of the omited ammonium nitrate fraction in all cases where the percentage of ammonium nitrate is reduced below 90%.

Included among the preferred substitute ingredients are alkali nitrates, such as sodium nitrate and potassium nitrate. Also included are wood flakes, expanded perlite, expanded shale and vermiculite, as well as certain heavy materials or indensifying agents later to be described.

The grain size distribution of the alkali nitrate ingredient is selected in dependence upon the intended use of the explosive. For example, for standard, so-called quarry powders, either for bag loading or air gun loading, bag run Chilean sodium nitrate is preferably used, a typical screen analysis of the Chilean nitrate being as follows: plus 8, 10%; minus 8 plus 10, 20%; minus 10 plus 14, 36%; and minus 14, 34%.

Where, on the other hand, the explosive is produced in the form of underground stick powders, for example, bag run Arcadian 3x sodium nitrate is preferably used, the prill size analysis in such case being typically as follows: plus 14, 43%; minus 40 plus 60, 41.4%; and minus 60, 15.6%.

To recapitulate, where an explosive is to be produced having a explosive equivalent, the following example illustrate a typical composition:

Example 2 Percent Ammonium nitrate 75 Metal activator 6 Nitro-body modifying agent 4 Carbonaceous combustible agent 1 Sodium nitrate 14 Total ,For an explosive having 50% strength, the following composition is used:

Example 3 Percent Ammonium nitrate 50 Metal activator 6 Nitro-body modifying agent 4 Combustible carbonaceous material 1 Sodium nitrate 39 Total 100 Similarly, for an explosive equivalent of 40%, which is approximately the lowest commercially used percentage, the following composition is used:

Example 4 Percent Ammonium nitrate 40 Metal activator 6 Nitro-body modifying agent 4 Combustible carbonaceous material 1 Sodium nitrate 49 Total 100 Still another important contribution to the art is the discovery that in the case of standard quarry powders, i.e. explosives customarily used in quarrying and highway construction, for example, and where a lower grade of explosive is desired, the substitution of expanded perlite, expanded shale, vermiculite or other highly porous rock, in predetermined quantities, affords many advantages. Wood flake is also used as a substitute under certain conditions later to be described.

In other words, conditions are frequently encountered in the field where it is desirable that the rock fragments produced by an explosive in a rock wall face, for example, remain substantially in situ and that they not be thrown any distance. So also, as in highway construction where rocks are frequently intermixed with dirt, or earth, a low grade explosive is preferable since it merely heaves or lifts the rock and dirt mixture, thereby loosening the rocks and dirt but allowing the loosened material to remain substantially in situ for more convenient and ready removal by suitable earth moving equipment.

A high grade explosive in these situations is undesirable since an explosive of this kind tends to result in widespread dispersion of rock fragments with attendant diiiiculty in gathering up and removing the same.

By substituting certain highly porous rock materials, such as expanded perlite, in the range of 3% to 12% by weight, as a substitute for the corresponding amount of sodium nitrate, it has been found that the explosive grade can be adjusted, or modified, to meet the requirements of the job to be performed.

The degradation caused by substituting only 3% expanded perlite is considerably less than that caused by substituting a 12% amount.

*Customarily, the substitution of expanded perlite is resorted to only where the desired explosive equivalent is 60% or less. To give some indication as to the effect of the substitution, where, for example, the strength is 60%, the substitution of 3% expanded perlite has but little effect on the percentage of explosive equivalent; Where, however, a substitution of 12% expanded perlite is used, the explosive equivalent drops to approximately 58%.

As is well-known, expanded perlite is a lightweight aggregate of siliceous volcanic glass expanded by heat for use where lightness of weight is desired, as in plaster, mortar and concrete. In the instant case, however, the low specific gravity of the perlite is subordinate to the unique property it possesses with respect to its deeply and intricately sculptured channels running throughout the material. These multitudinous channels afford lodgments or traps for a certain amount of the active explosive ingredients, the effect being to slow down, to some extent, the various explosion dynamics which combine to yield the over-all explosive strength and grade.

In summary, depending upon the particular condition encountered in the field, the substitution of an appropriate percentage of expanded perlite in quarry powders having an explosive equivalent of approximately 60% or less results in a desirable lower grade explosive composition which is not only inexpensive, but is accurately reproduceable.

Preferably, the grain size of the expanded perlite is minus 8 and plus 10 mesh, Tyler Sieve size. Granules of this size range afford many channels within which the metal activator and the ammonium nitrate particles can lodge, whereas perlite grains which are too small do not provide sufficient channels for optimum results.

Under certain field conditions, especially Where oxygen balance is a factor, wood flakes are utilized as a substitute ingredient in lieu of expanded perlite. Exemplary of such conditions are underground shots where additional oxygen is desired. Wood flakes are capable of providing the necessary oxygen, while duplicating to an extent the explosive degradation characteristics of expanded perlite.

An additional important contribution of the present invention is the utilization of certain materials, termed heavy materials or indensifying agents which added to the composition in small amounts to increase the specific gravity of the explosive to exceed 1.0, thus permitting submerged use of the product in wet bore holes, for marine usage etc. The term indensifying agents refers to materials which increase the density or specific gravity of the composition.

The indensifying agents are selected from minerals which are relatively chemically inert and are compatible with the other ingredients, and which preferably possess a specific gravity in the range of 4.0 to 8.0 Exemplary of such minerals are barite, garnet, ferrosilicon, magnetite and the like.

The selected material, such as barite or magnetite, is reduced to a grain size of minus plus Tyler Sieve size, it having been found that if the size is too small, the particles act as inhibitors, whereas granules larger in size tend to separate out by gravity, from the other ingredients. Ordinarily, only about 1% by weight of a heavy material is sufiicient to increase the specific gravity of the composition to an amount in excess of 1.0.

It can therefore be seen that I have provided an explosive composition wherein the explosive equivalent can be accurately achieved by using a direct one to one percentage ratio of ammonium nitrate having a critical gr in size distribution; wherein the explosive characteristics can be modified by the suitable substitution of inexpensive ingredients such as sodium nitrate, expanded perlite, expanded shale, vermiculite, and wood flakes; and wherein the specific gravity of the explosive composition can readily be altered by use of certain indensifying agents to permit of marine and wet bore hole usages.

What is claimed is:

1. In an explosive composition consisting essentially of NH NO a metal, a nitrated organic compound, and combustible carbonaceous material, the improvement comprising said nitrate having a Tyler Sieve grain size distribution of 78% passing a 150 mesh screen and 22% passing a mesh screen and retained by a mesh screen.

2. An explosive composition as in claim 1 wherein said metal activator is aluminum powder.

3. An explosive composition as in claim 1 wherein said nitrobody modifying agent is dinitrotoluene.

4. An explosive composition as in claim 1 wherein said combustible carbonaceous material is granular cork.

5. An explosive composition as in claim 1 wherein said combustible carbonaceous material is wood meal.

6. An explosive composition as in claim 1 wherein said ammonium nitrate percentage numerically equals saidexplosive equivalent when said explosive equivalent is in a range of 40% to 90%; and wherein the percentage balance consists of an alkali nitrate.

7. An explosive composition as in claim 6 wherein said alkali nitrate has a Tyler Sieve grain size distribution of approximately 10% plus 8, 20% minus 8 plus 10, 36% minus 10 plus 14, and 34% minus 14.

8. An explosive composition as in claim 6 wherein said alkali nitrate has a Tyler Sieve grain size distribution of approximately 43% plus 14, 41.4% minus 40 plus 60, and 15.6% minus 60.

9. An explosive composition as in claim 6 wherein expanded, highly porous rock material in a percentage range of about 3% .to 12% is substituted for a corresponding portion of said alkali nitrate.

10. An explosive composition as in claim 6 further characterized by the addition of a relatively chemically inert mineral compatible with the other ingredients and having a specific gravity in the approximate range of 4.0 to 8.0 in an amount sufiicient to raise the specific gravity of said composition in excess of 1.0.

References Cited UNITED STATES PATENTS 1,113,275 10/1914 WOOdbury 149112 X 2,069,612 2/1937 Kirst et al. 149-112 X 2,398,071 4/1946 Barab 149112 X 2,589,532 3/1952 Byers 14938 X 3,095,335 6/1963 McCloud et al. 1491l2 X 3,252,843 5/1966 Grifiith et a1. 1491l2 X L. DEWAYNE RUTLEDGE, Primary Examiner.

BENJAMIN R. PADGET'I, Examiner.

70 S. I. LECHERT, JR., Assistant Examiner. 

